State prosecutors in the western city of Dortmund said on Thursday charges had been filed against Samuel Kunz, 88, for assisting in the murder of Jews at Nazi death camp Belzec near the Polish city of Lublin between January 1942 and July 1943.

Because Kunz was under 21 at the start of the period under investigation, the trial will probably be held in the youth chamber of a court in nearby Bonn, prosecutors said. No date has been set for the trial.

Kunz's case came to light during investigations into Ukrainian-born John Demjanjuk, who went on trial in Munich last year, charged with helping to kill 27,900 Jews in the Holocaust.

Like Demjanjuk, Kunz was born in what became the Soviet Union and served in the Red Army, becoming a camp guard after his capture by the Germans, prosecutors said.

Kunz is number three on the Simon Wiesenthal Center's list of most wanted Nazi war criminals. The charges against him sent out a powerful signal that perpetrators would be brought to justice, said the Center's chief Nazi-hunter Efraim Zuroff.

"We have an obligation to the victims of the Holocaust to prosecute the people who turned them into victims," Zuroff told Reuters. "And Kunz is one of those people."

Kunz appears to have remained unknown until recently because he was not an officer -- previously the focus of German investigators, said Zuroff, who has just written a book on the subject.

"He was totally under the radar screen in Germany. The good news is that prosecutors have become more proactive," he said.

After the war Kunz became a civil servant, Zuroff said.

Belzec was one of the camps created for Operation Reinhard, one of the most ruthless phases in the mass killing of Jews.

Kunz's trial would help to shed light on Belzec, which had remained relatively obscure because so few people survived the camps used for Operation Reinhard, said Zuroff.

"The only purpose of the camps was extermination," he said. "For anyone who arrived there in the morning it was 99.9 percent sure they'd be dead in the evening."